This application is based on and claims priority from Korean Patent Application No. 2003-38515, filed on Jun. 14, 2003, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to image signal processing, and more particularly, to a method and apparatus for determining whether an input image is a film image.
2. Description of the Related Art
Images for films, televisions (TVs), digital video discs (DVDs) and so on have different frame structures. A film image has 24 progressive frames per second, while a TV or DVD video image has 60 interlaced fields per second. Therefore, to broadcast a film for display on a TV set, 24 progressive frames per second have to be converted into 60 interlaced fields per second. This conversion is made using a telecine operation. A 3:2 pull-down technique is employed during the telecine operation to convert film images into National Television System Committee (NTSC) TV images.
FIG. 1 is a diagram for explaining the conversion of 24 film frames per second into 60 fields per second using a 3:2 pull-down process.
Referring to FIG. 1, a top field 111 and a bottom field 112 are first extracted from one frame 110. Thereafter, another top field 113 is extracted from the frame 110. Next, a bottom field 121 and a top field 122 are extracted from a next frame 120. Through this procedure, two progressive frames are converted into five interlaced fields. Alternatively, after a bottom field 131, a top field 132 and a bottom field 133 are extracted from a frame 130, a top field and a bottom field are extracted from a next frame. Similarly, two progressive frames can also be converted into five interlaced fields through this procedure.
Once film images are converted into 60 interlaced fields using the above-described 3:2 pull-down process, the interlaced fields can be converted into 60 progressive frames by combining top fields and bottom fields.
FIG. 2 is a diagram for explaining the conversion of interlaced fields into progressive frames.
Images converted using the 3:2 pull-down process can be converted into progressive frames by combining top fields and bottom fields. In this case, an improved image quality can be obtained and a soft moving image can be obtained in a slow motion mode. Since films are stored at 24 frames per second, instead of 60 fields per second, a waste of storage space is prevented. However, different processing can be performed according to kinds of input images only after determining whether input images are images converted using the 3:2 pull-down technique or images having originally interlaced fields. Such a detection of characteristics of an image source is necessary not only for NTSC image signals but also for Phase Alternation Line (PAL) image signals and other types of image signals.
Conventional methods of determining whether received images are film images are divided into two methods according to the type of image information used in the determination process. A first method utilizes a pattern of a sum of absolute differences (SAD) between fields having the same characteristics calculated for every two-fields (one frame). More particularly, the first method is sub-divided into a variant which utilizes the fact that a period of values of the SAD is 5, and another variant which utilizes the fact that a period of difference signals between values of a current SAD and values of a previous SAD is 5 to obtain a SAD pattern having a higher periodicity.
A second method is to use the characteristics of a moving pattern between two fields. More particularly, the second method is sub-divided into a first variant which utilizes the fact that when a sum of motion vectors from blocks is added to a previously calculated sum, the result should be within a predetermined range, and a second variant of detecting a film image by obtaining a movement degree of a pixel, adding movement degrees of all the pixels to obtain a movement degree in the entire fields, converting a signal representative of the movement degree into a digital pattern, and comparing the converted pattern with a predetermined binary sequence of, for example, 100010.
However, neither of the conventional methods lead to patterns having an exact period. Furthermore, the conventional methods are disadvantageous in that a determination result of whether received images are film images varies depending on a threshold value, i.e., a reference value used during the conversion into digital patterns.